The present invention relates to a video signal control apparatus that controls a video signal from a television tuner, a VTR (video tape recorder) or the like to adjust the conditions of a video image indicating information of the video signal.
Typically, a signal processing device for use in a television, VTR, etc. employs the system that separates a video signal into a color signal and a luminance signal, which are in turn subjected to separate signal processings, and then mixes these processed signals to provide a composite video signal to be output to a CRT (cathode ray tube). Based on control data generated by a viewer controlling a video operation unit, a color signal processing unit performs color control while a luminance signal processing unit performs contrast control and brightness control. The luminance signal processing unit varies the AC component (amplitude) of the luminance signal to control the contrast and then causes a DC reproduction circuit to control the brightness.
When the contrast control is effected by considerably varying the amplitude of the luminance signal, however, the large change in amplitude is likely to vary the DC level of the luminance signal where the amplitude control is effected. The change in DC level of the luminance signal causes a partial brightness change on the screen so that a portion or some portions of the screen appears brighter or darker than other portions. This phenomenon occurs due to a delay in pedestal level control when the amplitude of the luminance signal is greatly changed. The delay in the pedestal level control results from the fact that the time constant of the DC reproduction circuit is typically set large in order to suppress a change in the brightness of the screen in a horizontal period.